Method of making an optical fiber having an imparted twist

ABSTRACT

An optical fiber is rolled by a swing motion of a swing guide roller in order to impart a predetermined twist to it effectively, and its polarization dispersion is suppressed equivalently as in a perfectly circular concentric optical fiber. A method of manufacturing such an optical fiber is also provided. As a swing guide roller swings, the optical fiber is rolled on its roller surface, so that a clockwise twist and a counterclockwise twist are imparted to the optical fiber alternately. At this time, the optical fiber is fitted in a V-shaped narrow groove formed at the central portion of the roller surface of a next-stage first stationary guide roller provided just beside the swing guide roller. Rolling of the optical fiber on the roller surface of the first stationary guide roller is suppressed, thereby helping smooth rolling of the optical fiber on the roller surface of the swing guide roller. As a result, a twist can be imparted to the optical fiber highly efficiently in accordance with the swing speed of the swing guide roller.

RELATED APPLICATION

This is a Continuation-in-part application of application Ser. No.08/609,830 filed on Mar. 1, 1996, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical fiber and a method ofmanufacturing the same. The present invention can be applied to a 1.3-μmsingle-mode ribbon fiber, a dispersion-shifted fiber, and adispersion-compensated fiber, as well as any other types of opticalfibers and their manufacturing methods, and is particularly suitable toa dispersion-compensated fiber having a high Ge content in its core,concretely, a dispersion-shift fiber(DSF) and a dipsersion-flatfiber(DFF) having a GeO₂ content at about 0.5 to 1.0% in their cores,and a dispesion-compensation fiber(DCF) having a GeO₂ content at about 1to 3% in its core and a fiber for an optical amplifier and large PMD(Polarization Mode Dispersion: also called merely "polarizationdispersion"), and a method of manufacturing the same.

2. Related Background Art

In a conventional optical fiber manufacturing method in which one end ofan optical fiber preform is softened by heating and an optical fiber isdrawn from it, it is difficult to make the core portion of the opticalfiber and a cladding portion around the core portion to have perfectlycircular and concentric sections, and the sections of the core portionand cladding portion usually become slightly elliptic or slightlydistorted circular. Accordingly, the refractive index distribution inthe sectional structure of the optical fiber is not completely uniform,which causes a difference in group velocity of two orthogonallypolarized waves in the section of the optical fiber, thereby undesirablyincreasing polarization dispersion. For this reason, when the opticalfiber is put into a practical use as a submarine cable or trunk cablethat require large-capacity, long-distance transmission, the adverseinfluence of the polarization dispersion appears largely. Even inoptical fibers having almost the same diameter, the higher the contentof the dopant, e.g., GeO₂, added to the core, the larger thepolarization dispersion.

SUMMARY OF THE INVENTION

It is an object of the present invention to effectively impart apredetermined twist to an optical fiber by rolling the optical fiber onthe roller surface of a guide roller in accordance with the swing motionof the guide roller, thereby providing an optical fiber in which, evenif the sectional shapes of its core portion and cladding portion are notperfectly circular and concentric, polarization dispersion can besuppressed in the elongated optical fiber as a whole equivalently as ina case wherein the sections of the core portion and the cladding portionare perfectly circular and concentric, and a method of manufacturing thesame.

The present invention relates to an optical fiber manufacturing methodcomprising the first step of drawing an optical fiber from an opticalfiber preform, the second step of coating the optical fiber with apredetermined coating material, and the third step of imparting apredetermined twist to the optical fiber coated with the predeterminedcoating material. The third step further comprises the first substep ofguiding the optical fiber coated with the predetermined coating materialwith a first guide roller that swings periodically, and rolling theoptical fiber on a roller surface of the first guide roller inaccordance with swing of the first guide roller, and the second substepof guiding the optical fiber that has passed through the first guideroller with a second guide roller provided to a next stage of the firstguide roller and having a fixed rotating shaft, and suppressing theoptical fiber from rolling on a roller surface of the second guideroller with an optical fiber rolling suppression means provided to thesecond guide roller.

The optical fiber rolling suppression means provided to the second guideroller is preferably a V-shaped, U-shaped, or convex narrow groove whichis formed in the roller surface of the second guide roller to fit theoptical fiber in it.

It is preferable that the outer diameter and position of each of thefirst and second guide rollers be adjusted so that a length with whichthe optical fiber contacts the roller surface of the first guide rolleris substantially equal to or less than a roller circumferencecorresponding to a central angle of 90° of the first guide roller.

It is preferable that the roller surface of the first guide roller withwhich the optical fiber contacts be covered with a resin having a highcoefficient of friction against the predetermined coating material ofthe optical fiber.

The resin to cover the roller surface of the first guide roller ispreferably an urethane resin or an acrylic resin.

The optical fiber preferably has a drawing tension of 4.0 kg/mm² or moreand 16 kg/mm² or less.

The third step preferably further comprises the substep of suppressingresponsive motion of the optical fiber, which is caused by swing of thefirst guide roller, with an optical fiber responsive motion suppressingmeans provided on a preceding stage of the first guide roller.

It is preferable that the optical fiber responsive motion suppressingmeans be at least a pair of guide rollers which are provided above thefirst guide roller at a predetermined distance to oppose each other at apredetermined gap through which the optical fiber is passed.

Further, it is another object of the present invention to provide anoptical fiber drawing method for reducing polarization characteristic ofan optical fiber, comprising the steps of: drawing the optical fiberfrom an optical fiber preform; coating the optical fiber with apredetermined coating material; and guiding the optical fiber coatedwith the predetermined coating material with a first guide roller thatswings periodically, and rolling the optical fiber on a roller surfaceof the first guide roller in accordance with swing of the first guideroller; and guiding the optical fiber that has passed through the firstguide roller with a second guide roller provided to a next stage of thefirst guide roller and having a fixed rotating shaft and suppressing theoptical fiber from rolling on a roller surface of the second guideroller with an optical fiber rolling suppression portion provided to thesecond guide roller, wherein the swing of the first guide roller is suchthat the maximum clockwise angle and the maximum counterclockwise angleof the first guide roller are equal, that a period of the clockwiseswing which is the time from the beginning to the end of the clockwiseswing of the first guide roller and a period of the counterclockwiseswing which is the time from the beginning to the end of thecounterclockwise swing of the first guide roller are equal, and that aswing direction of the first guide roller is reversed smoothly withoutstopping when the swing angle of the first guide roller becomes maximum.

It is preferable in the above method that an optical fiber responsivemotion suppressing means is provided to a preceding stage of the firstguide roller, the means comprises two pairs of guide rollers which areprovided above the first guide roller at a predetermined distance, theguide rollers belongs to each pair opposing each other at apredetermined gap through which the optical fiber is passed, anddirection of a roller shaft of one of the two pairs of guide rollers isperpendicular to direction of a rolling shaft of the other of the twopairs of guide rollers.

It is prefeable that width of the roller surface of the first guideroller on which the optical fiber can be rolled, is not less than 3 mm.

It is preferable that the first guide roller has flanges at both sidesof the roller surface, and the optical fiber does not come into contactwith the flanges when the swing angle of the first guide roller becomesmaximum.

It is more further object of the present invention to provide anapparatus used by an optical fiber drawing method comprising: a base; apinion gear rotatably supported about a shaft by the base, the shaftbeing perpendicular to the rotating shaft of the first guide roller andpassing through substantially center of the first guide roller; a rackgear meshing with the pinion gear; a first movable portion linearlymoving as against the base in a direction perpendicular to a directionof the rotating shaft of the pinion gear, the rack gear being fixed tothe first movable portion; a second movable portion linearly moving asagainst the first movable portion is a direction perpendicular to bothdirection of linear moving of the first movable portion and thedirection of the rotating shaft of the pinion gear; and a motor rotatingat constant velocity and giving a rotating motion with constant velocityas against the base to the second movable portion.

It is preferable in the above apparatus that materials of the rack gearand the pinion gear are different from each other.

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not to beconsidered as limiting the present invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process view showing an optical fiber manufacturing method;

FIGS. 2 to 5 are views for explaining how to impart a twist to anoptical fiber;

FIG. 6 is a process view showing an optical fiber manufacturing methodaccording to the present invention;

FIG. 7 is a view showing a swing guide roller and a first stationaryguide roller of FIG. 6 when viewed from the above;

FIG. 8 is a view showing a pair of guide rollers for optical fiberresponsive motion control and the swing guide roller when viewed fromthe side;

FIG. 9 is a graph for explaining the relationship between thepresence/absence of the optical fiber rolling prevention means of thefirst stationary guide roller and the polarization dispersion of theoptical fiber;

FIG. 10 is a view showing the positions of the swing guide roller andfirst stationary guide roller relative to each other;

FIG. 11 is a graph showing the relationship between the position shownin FIG. 10 and the polarization dispersion of the optical fiber;

FIG. 12 is a graph for explaining the relationship between the materialof the roller surface of the swing guide roller and the polarizationdispersion of the optical fiber;

FIG. 13 is a graph for explaining the relationship between the fibertensile force and the rolling properties on the roller surface of theswing guide roller;

FIG. 14 is a diagram showing the installation position of the pair ofguide rollers for optical fiber responsive motion control relative tothe swing guide roller;

FIG. 15 is a graph for explaining the relationship between the gapbetween the pair of guide rollers and the polarization dispersion of theoptical fiber; and

FIG. 16 is a perspective view of a mechanism that swings the swing guideroller such that the swing angle changes sinusoidally.

FIGS. 17A, 17B, 17C and 17D are plan views of the mechanism shown inFIG. 16 in each status in the drawing of the optical fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to solve the problem of polarization dispersion in the priorart technique described above, an optical fiber manufacturing method hasbeen proposed (see Japanese Patent Laid-Open No. 6-171970) in which,after an optical fiber is drawn from an optical fiber preform and iscoated with a predetermined coating material, the optical fiber isguided by a guide roller whose rotating shaft swings periodically,thereby imparting a predetermined twist to the optical fiber.

The outline of this optical fiber manufacturing method will be describedwith reference to FIGS. 1 and 2. FIG. 1 is a manufacturing process viewfor explaining the optical fiber manufacturing method, and FIG. 2 is aview for explaining how to impart a twist to the optical fiber.

As shown in FIG. 1, an optical fiber preform 300 is fed into a drawingfurnace 310 to be softened by heating in the drawing furnace 310. Anoptical fiber 320 is drawn from one end of the softened optical fiberpreform 300. The drawn optical fiber 320 is passed through a coatingunit 340 via a diameter monitor 330, to be coated with a polymer coatingby the coating unit 340. Then, the optical fiber 320 is sequentiallypassed through a coating concentricity monitor 350, a coating resinsetting unit 360 having, e.g., a UV lamp, and a coating diameter monitor370.

Subsequently, the optical fiber 320 enters a zone 400 having first tothird guide rollers 381, 382, and 383 and a tensile capstan 390 thatpulls the optical fiber 320 with a predetermined force. The rotatingshaft of the first guide roller 381 swings about an axis parallel to atensile tower axis, which is the characteristic feature of thismanufacturing method. The rotating shafts of the second guide roller 382provided on the next stage of the first guide roller 381 and the thirdguide roller 383 provided on the next stage of the second guide roller382 are fixed.

As shown in FIG. 2, when, for example, the first guide roller 381 istilted about an axis parallel to the tensile tower axis by an angle θ, alateral force on the sheet of FIG. 2 is applied to the optical fiber 320by this tilt, and the optical fiber 320 rolls on the roller surface ofthe first guide roller 381. When this rolling is transmitted to theheated portion of the preform, a twist is imparted to the optical fiber320 about a longitudinal axis. Subsequently, the first guide roller 381is restored to the initial state. In this manner, when asymmetricreciprocal swing motion of the first guide roller 381 from an angle 0 toan angle +θ, as indicated by a double-headed arrow in FIG. 2, isrepeated, a twist is imparted to the optical fiber 320 intermittently.

The swing motion of the first guide roller 381 is not limited to thatshown in FIG. 2, but can be symmetric reciprocal motion of 2θ from anangle -θ to the angle +θ about an axis parallel to the tensile toweraxis, or can be symmetric reciprocal motion in the direction of therotating shaft of the first guide roller 381. In these cases, aclockwise twist and a counterclockwise twist with respect to thetraveling direction are alternately imparted to the optical fiber 320.

As described above, according to the proposed optical fibermanufacturing method, since a twist is imparted to the optical fiber 320intermittently or alternately, the optical fiber 320 can be provided inwhich, even if the sectional shapes of its core portion and claddingportion are not perfectly circular and concentric, polarizationdispersion is suppressed in the elongated optical fiber as a wholeequivalently as in a case wherein the core portion and the claddingportion are perfectly circular and concentric.

In the above optical fiber manufacturing method, however, due to theswing motion of the first guide roller 381, the optical fiber 320 cannotroll on the roller surface smoothly, and thus a predetermined twistcannot be effectively imparted to the optical fiber 320.

This point will be clarified with reference to FIGS. 3 to 5. FIG. 3 is aschematic view of the guide portion of an optical fiber manufacturingapparatus, FIG. 4 shows the first guide roller of FIG. 3 when viewedfrom the above, and FIG. 5 shows the first guide roller of FIG. 4 whenviewed from the side.

As shown in FIG. 3, the rotating shaft of the first guide roller 381swings about an axis parallel to the tensile tower axis. The secondguide roller 382, which is located on the next stage of the first guideroller 381 and which has a fixed rotating shaft, is provided at aposition relatively higher than that of the first guide roller 381.Accordingly, in FIG. 3, an optical fiber 321 fed from the drawingfurnace is brought into contact with the first guide roller 381 alongthe right side surface, the bottom surface, and the left side surface ofthe first guide roller 381, and is separated, as an optical fiber 322,from the left side surface of the swing roller 381 and fed to the secondguide roller 382. The length with which the optical fiber contacts theroller surface of the first guide roller 381 exceeds a rollercircumference corresponding to a central angle 90°. Although not shownin FIG. 3, the roller width of the second guide roller 382 is the sameas that of the first guide roller 381, in the same manner as in the caseshown in FIG. 2.

A case wherein the optical fiber 320 is guided by the swingable firstguide roller 381 under these conditions will be described.

As shown in FIGS. 4 and 5, in a state wherein the first guide roller 381is tilted by the angle +θ, the optical fiber 321 that has gone near theright side surface of the first guide roller 381 from the drawingfurnace 310 starts to be brought into contact with the roller surface ofthe first guide roller 381 from its right side surface, is kept incontact with it along its bottom surface until going near its left sidesurface, is then separated from it and is fed as the optical fiber 322toward the second guide roller 382 on the next stage.

When the first guide roller 381 is restored to the initial state fromthis state, on the right side surface of the first guide roller 381, anoptical fiber 321a rolls on the roller surface counterclockwise withrespect to the traveling direction, and is to go near the position of anoptical fiber 321b. Meanwhile, on the left side surface of the firstguide roller 381, an optical fiber 322a rolls on the roller surfaceclockwise with respect to the traveling direction, and is to go near theposition of an optical fiber 322b. In this manner, on the right and leftside surfaces of the first guide roller 381, the rolling directions areopposite to each other, thereby interfering with rolling.

Accordingly, the counterclockwise rolling for changing the optical fiber321a to the optical fiber 321b on the right side surface of the firstguide roller 381 is interfered by the clockwise rolling for changing theoptical fiber 322a to the optical fiber 322b on the lft side surface ofthe first guide roller 381, so that the optical fiber partially slideson the first guide roller. Therefore, while a counterclockwise twist issupposed to be imparted to the optical fiber 320 in the travelingdirection in accordance with rolling for changing the optical fiber 321ato the optical fiber 321b, it cannot be effectively imparted inpractice.

The reason for this is as follows. First, as the second guide roller 382is provided at a position higher than that of the first guide roller381, the optical fiber 320 is brought into contact with not only theright side surface of the first guide roller 381 but also its left sidesurface, so that rolling of the optical fiber occurring on the left sidesurface interferes with rolling on the right side surface. Second, sincethe roller width of the second guide roller 382 is equal to that of thefirst guide roller 381, the optical fiber 320 can roll on the rollersurface of the second guide roller 382 as well, so that rolling of theoptical fiber 320 on the left side surface of the first guide roller 381cannot be suppressed. Also, rolling of the optical fiber 320 on thesecond guide roller 382 has an effect similar to that on the left sidesurface of the first guide roller 381, thereby interfering with rollingon the right side surface of the first guide roller 381.

In the conventional case shown in FIG. 1, as the first swing guideroller 381 and the second guide roller 382 on the second stage areprovided at the same level, the first cause that interferes with theeffective twist imparted to the optical fiber 320 is solved. However, assecond cause that the second guide roller 382 has the same roller widthas that of the first guide roller 381 and that the optical fiber 320 canroll on the roller surface of the second guide roller 382 is left, it isstill difficult to realize to effectively impart a twist to the opticalfiber 320.

In the optical fiber manufacturing method of the present invention, anoptical fiber is drawn from an optical fiber preform, the optical fiberis coated with a predetermined coating material, and a predeterminedtwist is imparted to the optical fiber coated with the predeterminedcoating material. In this case, the predetermined twist is imparted tothe optical fiber by a combination of the substep of guiding the opticalfiber with a first guide roller whose rotating shaft swingsperiodically, and rolling the optical fiber on a roller surface of thefirst guide roller, and the substep of guiding the optical fiber thathas passed through the first guide roller with the second guide rollerprovided to a next stage and having a fixed rotating shaft andsuppressing the optical fiber from rolling on a roller surface of thesecond guide roller with an optical fiber rolling suppression meansprovided to the second guide roller.

More specifically, when the optical fiber rolls on the roller surface ofthe first guide roller that swings, a predetermined twist is imparted tothe optical fiber. At this time, if the optical fiber is let to freelyroll on the roller surface of the second guide roller on the next stage,rolling of the optical fiber on the first guide roller is interferedwith, and a twist is not effectively imparted to the optical fiber. Forthis reason, rolling of the optical fiber on the roller surface issuppressed by the optical fiber rolling suppression means provided tothe second guide roller, so that a twist is highly efficiently impartedto the optical fiber by the first guide roller in accordance with theswing speed of the first guide roller. As a result, a twist can beeffectively imparted to the optical fiber by the combination of thefirst guide roller that swings and the second guide roller provided withthe optical fiber rolling suppression means.

An example of the optical fiber rolling suppression means provided tothe second guide roller includes a V-shaped, U-shaped, or concave narrowgroove which is formed in the roller surface. When the optical fiber isfitted in this narrow groove and guided, rolling of the optical fibercan be suppressed.

If the length with which the optical fiber contacts the roller surfaceof the first guide roller exceeds a roller circumference correspondingto a central angle 90°, the rolling direction of the optical fiber on aside where the optical fiber starts to be in contact with the roller andthe rolling direction thereof on a side where the optical fiber isseparated from the roller become opposite to each other. Since a rotarymotion aiming at imparting a twist to the optical fiber is interferedwith, a twist cannot be effectively imparted to the optical fiber.Therefore, the outer diameter and position of each of the first andsecond guide rollers are adjusted so that a length with which theoptical fiber contacts the roller surface of the first guide roller issubstantially equal to or less than a roller circumference correspondingto a central angle 90° of the first guide roller, thereby imparting atwist to the optical fiber effectively.

The twist to be imparted to the optical fiber is generated as theoptical fiber rolls on the roller surface of the first guide roller.Hence, in order to realize ideal rolling of the optical fiber free fromsliding on the roller surface, the coefficient of friction between thepredetermined coating material of the optical fiber and the rollersurface must be high. Accordingly, if the roller surface of the firstguide roller with which the optical fiber is brought into contact iscovered with a resin, e.g., an urethane resin or an acrylic resin,having a high coefficient of friction against the predetermined coatingmaterial of the optical fiber, the optical fiber can be rolled on theroller surface in an ideal manner, thereby imparting a twist to theoptical fiber effectively.

In order to increase the frictional force on the roller surface of thefirst guide roller that acts on the predetermined coating material ofthe optical fiber, it is also effective to increase the drawing tension,thereby increasing the force with which the predetermined coatingmaterial of the optical fiber is urged against the roller surface of theroller. An increase in rolling properties achieved by an increase infrictional force appears when the optical fiber has a drawing tension of4.0 kg/mm² or more. If the drawing tension exceeds 16 kg/mm², fiberdisconnection occurs. Hence, the drawing tension must be 16 kg/mm² orless.

As the first guide roller swings, the optical fiber immediately beforebeing brought into contact with the roller of the first guide rollerresponds. If this responsive motion of the optical fiber is left, theamount of twist to be imparted to the optical fiber may be decreased, orthe thickness of the coating of the optical fiber may becomenon-uniform. Accordingly, the responsive motion of the optical fiber issuppressed by the optical fiber responsive motion suppressing meansprovided to a preceding stage of the first guide roller, therebypreventing a decrease in amount of twist imparted to the optical fiberand a non-uniformity in thickness of the coating of the optical fiber.

An example of the optical fiber responsive motion suppressing meansincludes at least a pair of guide rollers which are provided above thefirst guide roller at a predetermined distance to oppose each other at apredetermined gap through which the optical fiber is passed. When theoptical fiber responds to the swing of the first guide roller by atleast the pair of guide rollers, if the responsive motion of the opticalfiber is within a predetermined range, the optical fiber passes betweenat least the pair of guide rollers. If the responsive motion exceeds thepredetermined range, the optical fiber will contact either one of theguide rollers, so that its further responsive motion is interrupted.Therefore, at least the pair of guide rollers serve as the optical fiberresponsive motion suppressing means.

The optical fiber according to the present invention comprises a coreportion and a cladding portion covering the core portion, is impartedwith a predetermined twist, and is characterized by being manufacturedin accordance with the above manufacturing method.

The optical fiber of the present invention is manufactured in accordancewith the above manufacturing method, has the core portion and thecladding portion covering the core portion, and is imparted with thepredetermined twist. Therefore, even if the sectional shapes of the coreportion and cladding portion of the optical fiber are not perfectlycircular and concentric, polarization dispersion can be suppressed inthe elongated optical fiber as a whole equivalently as in a case whereinthe core portion and the cladding portion are perfectly circular andconcentric. Since the non-uniformity in thickness of the coating of theoptical fiber is suppressed, the stress distribution on the section ofthe optical fiber can be prevented from being asymmetric, therebyincreasing the strength of the optical fiber when formed into a cable.

Embodiment 1

An example of the present invention will be described with reference tothe accompanying drawings. In the explanation of the drawings, the samereference numerals denote the identical elements, and a repetitiveexplanation thereof will be omitted.

FIG. 6 is a manufacturing process view of the optical fibermanufacturing method of the present invention.

As shown in FIG. 6, in the optical fiber manufacturing method of thisembodiment, an optical fiber preform 100 is prepared. The optical fiberpreform 100 is fabricated in accordance with a vapor-phase axialdeposition method (VAD method), an outside vapor-phase deposition method(OVD method), a modified chemical vapor deposition method (MCVD method),a rod-in-tube method, and the like.

After the optical fiber preform 100 is set in a drawing furnace 110, thelower end of the optical fiber preform 100 is softened by heating by aheater 120 in the drawing furnace 110, and an optical fiber 130 isobtained by drawing. A drawing velocity Vp for this is, e.g., 100 m/min.

The diameter of the optical fiber 130 obtained by drawing is measured bya laser diameter measurement unit 140. The measurement result isreported to a drawing control unit 150. The drawing control unit 150controls the heating temperature of the heater 120 and the drawingvelocity Vp based on the measurement result such that the diameter ofthe optical fiber 130 becomes a predetermined value, usually 125 μm.

The optical fiber 130 is passed through a liquid resin 171 stored in afirst resin coating die 161 to apply the first layer resin to itssurface. Successively, an UV lamp 181 irradiates the optical fiber 130applied with the first layer resin, thereby setting the first layerresin. The optical fiber 130 is then passed through a liquid resin 172stored in a second resin coating die 162 in the same manner to apply thesecond layer resin to the surface of its first layer resin.Successively, an UV lamp 182 irradiates the optical fiber 130 appliedwith the second layer resin, thereby setting the second layer resin. Inthis manner, an optical fiber 200 is formed by coating the surface ofthe optical fiber 130 with a resin coating 190 consisting of two resinlayers. The optical fiber 200 with the coating 190 has a diameter of,e.g., 250 μm.

Subsequently, the optical fiber 200 is passed between a pair of guiderollers 210 for optical fiber responsive motion suppression that rotatefreely in the traveling direction of the optical fiber 200, and issuccessively and sequentially guided with a swing guide roller 220, afirst stationary guide roller 231 provided on the next stage of theoptical fiber 200, and a second stationary guide roller 232 provided onthe next stage of the first stationary guide roller 231. Furthermore,the optical fiber 200 that has passed through the swing guide roller220, the first stationary guide roller 231, and the second stationaryguide roller 232 sequentially is taken up on a drum 240.

The pair of guide rollers 210 for optical fiber responsive motionsuppression are located at a position right above the optical fiber 200at a distance L=100 mm from it, and a gap d between the pair of guiderollers 210 is 2 mm. The swing guide roller 220 has an outer diameter of150 mm and a width of 30 mm. The material of the roller surface of theswing guide roller 220 is aluminum which is the material of the rolleritself, and the rotating shaft of the swing guide roller 220 swingsabout an axis parallel to the tensile tower axis with a period of 100rpm from an angle -θ to an angle +θ. The first stationary guide roller231 is provided at a position just beside the swing guide roller 220 ata distance D=250 mm, and has an outer diameter of 150 mm and a width of30 mm equal to those of the swing guide roller 220. However, therotating shaft of the first stationary guide roller 231 is fixed, and aV-shaped narrow groove serving as an optical fiber rolling suppressionmeans is formed at the central portion of the roller surface of thefirst stationary guide roller 231. With the combination of the pair ofguide rollers 210 for optical fiber responsive motion suppression, theswing guide roller 220, and the first stationary guide roller 231 thatare arranged under these conditions, a predetermined twist is impartedto the optical fiber 200 effectively, i.e., highly efficiently inaccordance with the swing speed of the swing guide roller 220. Thecharacteristic feature of this embodiment resides in this.

A method of imparting a predetermined twist to the optical fiber 200effectively will be described with reference to FIGS. 7 and 8. FIG. 7shows the swing guide roller 220 and the first stationary guide roller231 of FIG. 6 when viewed from the above, and FIG. 8 shows the pair ofguide rollers 210 for optical fiber responsive motion suppression andthe swing guide roller 220 when viewed from the side.

As shown in FIG. 7, when the swing guide roller 220 is tilted about anaxis parallel to the tensile tower axis by an angle +θ, a lateral forceis applied to the optical fiber 200 by this tilt to roll the opticalfiber 200 on the roller surface of the swing guide roller 220. A twistis imparted to the optical fiber 200 by this rolling. Subsequently, theswing guide roller 220 is tilted in the opposite direction by an angle-θ. When symmetric reciprocal motion in which the swing guide roller 220swings from the angle +θ to the angle -θ is repeated, as indicated by adouble-headed arrow in FIG. 7, a clockwise twist and a counterclockwisetwist in the traveling direction are alternately imparted to the opticalfiber 200.

As the first stationary guide roller 231 on the next stage of the swingguide roller 220 is provided just beside the swing guide roller 220 tohave the same outer diameter as that of the swing guide roller 220, thelength with which the optical fiber 200 contacts the roller surface ofthe swing guide roller 220 becomes substantially equal to the rollercircumference corresponding to the central angle 90° of the swing guideroller 220. More specifically, the optical fiber 200 contacts the swingguide roller 220 along one side surface to the bottom surface of theswing guide roller 220, and is separated from it at its lowest portion.Thus, the following drawback can be prevented: the optical fiber 200rolls on the other side surface of the roller to interfere with rollingof the optical fiber 200 on one side surface of the roller to cause theoptical fiber 200 to slide on the swing guide roller 220. Accordingly,with rolling of the optical fiber 200 on one side surface of the rollerof the swing guide roller 220, a twist can be imparted to the opticalfiber 200 highly efficiently in accordance with the swing speed of theswing guide roller 220.

A V-shaped narrow groove 250 serving as the optical fiber rollingsuppression means is formed at the central portion of the roller surfaceof the first stationary guide roller 231, and the optical fiber 200guided by the first stationary guide roller 231 is fitted in theV-shaped narrow groove 250. Thus, the following drawback can beprevented: the optical fiber 200 rolls on the roller surface of thefirst stationary guide roller 231 to interfere with rolling of theoptical fiber 200 on the swing guide roller 220 that aims at imparting atwist to the optical fiber 200. As a result, since rolling of theoptical fiber 200 on the roller surface of the first stationary guideroller 231 is suppressed by the V-shaped narrow groove 250, a twist canbe imparted to the optical fiber 200 highly efficiently in accordancewith the swing speed of the swing guide roller 220.

As shown in FIG. 8, when the swing guide roller 220 is tilted about theaxis parallel to the tensile tower axis by an angle +θ and the opticalfiber 200 rolls on the roller surface of the swing guide roller 220,together with rolling of the optical fiber 200, the optical fiber 200 onthe drawing furnace side immediately before the swing guide roller 220also responds to swinging in the swing direction of the swing guideroller 220. If the responsive motion of the optical fiber 200 exceeds apredetermined range, the amount of twist to be imparted to the opticalfiber 200 may be decreased, or the thickness of the optical fiber 200coated with the resin coating 190 may become non-uniform. However, asthe guide rollers 210 are provided immediately above the swing guideroller 220, when the responsive motion of the optical fiber 200 exceedsa predetermined value, the optical fiber 200 is brought into contactwith one of the pair of guide rollers 210, so that its furtherresponsive motion is prevented. Hence, when the pair of guide rollers210 suppress the responsive motion of the optical fiber 200, a decreasein amount of twist imparted to the optical fiber 200 and thenon-uniformity in thickness of the optical fiber 200 coated with theresin coating 190 can be suppressed.

In this manner, according to the optical fiber manufacturing method ofthis embodiment, as the pair of guide rollers 210 for optical fiberresponsive motion suppression, the swing guide roller 220, and the firststationary guide roller 231 are combined, the swing guide roller 220allows the optical fiber 200 to roll on its roller surface by its swingmotion to impart a clockwise twist and a counterclockwise twist to theoptical fiber 200 alternately, and the pair of guide rollers 210 foroptical fiber responsive motion suppression and the first stationaryguide roller 231 provided with the optical fiber rolling suppressionmeans help smooth rolling of the optical fiber 200 on the roller surfaceof the swing guide roller 220. As a result, a twist can be imparted tothe optical fiber 200 highly efficiently in accordance with the swingspeed of the swing guide roller 220.

According to the optical fiber manufacturing method of this embodiment,when letting the optical fiber 200 to roll on the roller surface of theswing guide roller 220, the responsive motion of the optical fiber 200can be suppressed by the pair of guide rollers 210 for optical fiberresponsive motion suppression. Thus, the non-uniformity in thickness ofthe optical fiber 200 coated with the resin coating 190 can besuppressed.

The optical fiber 200 according to the present invention is manufacturedin accordance with the above manufacturing method, has a core portionand a cladding portion covering the core portion, and is imparted with aclockwise twist and a counterclockwise twist alternately. Even if thesectional shapes of the core portion and cladding portion of the opticalfiber 200 are not perfectly circular and concentric, polarizationdispersion can be suppressed in the elongated optical fiber as a wholeequivalently as in a case wherein the core portion and the claddingportion are perfectly circular and concentric.

In the optical fiber 200 coated with the resin coating 190 of thepresent invention, since the non-uniformity in its thickness issuppressed, the stress distribution on the section of the optical fiber200 can be prevented from becoming asymmetric. Thus, the strength of theoptical fiber 200 when formed into a cable can be increased.

In the above embodiment, the swing motion of the swing guide roller 220is a symmetrically reciprocal motion from the angle -θ to the angle +θ,as shown in FIG. 7. However, the swing motion of the swing guide roller220 is not limited to this, but can be, e.g., an asymmetric reciprocalmotion in which the swing guide roller 220 swings from the zero angle tothe angle +θ. In this case, a twist is intermittently imparted to theoptical fiber 200. Also, the swing motion of the swing guide roller 220may be a symmetric reciprocal motion in which the swing guide roller 220swings in the direction of its rotating shaft. In this case, a clockwisetwist and a counterclockwise twist are imparted to the optical fiber 200alternately, in the same manner as in the above embodiment.

In the above embodiment, the V-shaped narrow groove 250 serving as theoptical fiber rolling suppression means is formed in the firststationary guide roller 231. However, the same effect can be obtained byforming a U-shaped or concave narrow groove instead.

An experiment conducted by the present inventors in order to confirm theeffects of the pair of guide rollers 210 for optical fiber responsivemotion suppression, the swing guide roller 220, and the first stationaryguide roller 231, which constitute the essential part of the aboveembodiment, and to obtain the optimum conditions for achieving theseeffects, and the result of the experiment will be described.

The first experiment aims at confirming the effect obtained by guidingthe optical fiber 200 with the first stationary guide roller 231provided with the optical fiber rolling suppression means. Morespecifically, a case wherein the V-shaped narrow groove 250 serving asthe optical fiber rolling suppression means was formed in the firststationary guide roller 231, and the optical fiber 200 was fitted in theV-shaped narrow groove 250 and guided, and a case wherein no opticalfiber rolling suppression means was provided to the first stationaryguide roller 231 and an optical fiber could be rolled on the rollersurface of the first stationary guide roller 231, were compared. Variousother conditions were the same as in the case described with referenceto FIGS. 6 and 7, except that the swing period of the swing guide roller220 was changed between 0 and 200 rpm.

The graph of FIG. 9 shows the result of the first experiment. As isapparent from this graph, when no optical fiber rolling suppressionmeans is provided to the first stationary guide roller 231 so that theoptical fiber can be rolled on the roller surface of the firststationary guide roller 231, even if the swing period of the swing guideroller 220 is changed, the polarization dispersion of the optical fiber200 is not decreased. In contrast to this, when the V-shaped narrowgroove 250 serving as the optical fiber rolling suppression means isformed in the first stationary guide roller 231, the polarizationdispersion of the optical fiber 200 is decreased in the entire swingperiod. This effect is conspicuous particularly in the swing period of20 to 150 rpm, the preferred swing period being 50 to 100 rpm.

Accordingly, it is confirmed from the first experiment that the firststationary guide roller 231 provided with the optical fiber rollingsuppression means helps the optical fiber 200 to roll smoothly on theroller surface of the swing guide roller 220, so that a twist isimparted to the optical fiber 200 highly efficiently in accordance withthe swing speed of the swing guide roller 220.

The second experiment aims at obtaining the optimum conditions of thepositions of the swing guide roller 220 and the first stationary guideroller 231 relative to each other. More specifically, as shown in FIG.10, by employing a horizontal distance D (D=180 mm, 250 mm, and 500 mm)between the swing guide roller 220 and the first stationary guide roller231 as the parameter, a relative height Δh (the downward and upwarddirections are defined as positive and negative, respectively) of thelowest portion of the first stationary guide roller 231 with respect tothe lowest portion of the swing guide roller 220 was changed. Thepolarization dispersion of the optical fiber 200 obtained in this casewas measured. Various other conditions were the same as in the casedescribed with reference to FIGS. 6 and 7.

The graph of FIG. 11 shows the result of the second experiment. As isapparent from this graph, when the relative height Δh of the lowestportion of the first stationary guide roller 231 with respect to thelowest portion of the swing guide roller 220 satisfies 0≦Δh<150 mm,i.e., when the lowest portion of the first stationary guide roller 231is of the same height as or relatively lower than the lowest portion ofthe first stationary guide roller 231, the polarization dispersion ofthe optical fiber 200 is decreased greatly as compared to a case whereinthe relative height Δh satisfies -150 mm<Δh<0, i.e., a case wherein thelowest portion of the first stationary guide roller 231 is relativelyhigher than the lowest portion of the swing guide roller 220. The largerthe horizontal distance D between the swing guide roller 220 and thefirst stationary guide roller 231, the larger the decrease inpolarization dispersion of the optical fiber 200. However, when therelative height Δh satisfies 0≦Δh<150 mm, the difference in polarizationdispersion is not so large.

The reason for this is as follows. When the relative height Δh satisfies0≦Δh<150 mm, the length with which the optical fiber 200 contacts theroller surface of the swing guide roller 220 becomes equal to or lessthan the roller circumference corresponding to the central angle 90°, sothat the optical fiber 200 is in contact with the swing guide roller 220along one side surface to the bottom surface of the swing guide roller220, and is separated from the swing guide roller 220 at the lowestportion of the swing guide roller 220 or immediately before it. Incontrast to this, when the relative height Δh satisfies -150 mm<Δh<0,the length with which the optical fiber 200 contacts the roller surfaceof the swing guide roller 220 exceeds the roller circumferencecorresponding to the central angle 90°, so that the optical fiber 200contacts the swing guide roller 220 along one side surface, the bottomsurface, and the other side surface of the swing guide roller 220. Morespecifically, in the latter case, since the optical fiber 200 rolls evenon the other side surface of the roller, rolling of the optical fiber200 on one side surface, which aims at imparting a twist to the opticalfiber 200, is interfered with. In contrast to this, in the former case,since such a situation does not occur, the optical fiber 200 can berolled smoothly, so that a twist can be imparted to the optical fiber200 highly efficiently in accordance with the swing speed of the swingguide roller 220.

Accordingly, from the second experiment, it is confirmed that thepositions of the swing guide roller 220 and the first stationary guideroller 231 relative to each other are preferably adjusted such that alength with which the optical fiber 200 contacts the roller surface ofthe first guide roller 220 is substantially equal to or less than aroller circumference corresponding to a central angle 90° of the firstguide roller.

In the above description, both the optical fiber 200 and the firststationary guide roller 231 have the same diameter. Even if thediameters are different, the object can be achieved by paying attentionto the relative height Δh of the lowest portion of the first stationaryguide roller 231 with respect to the lowest portion of the swing guideroller 220. This means that the length with which the optical fiber 200contacts the roller surface of the swing guide roller 220 can beadjusted also by changing the outer diameters of the swing guide roller220 and the first stationary guide roller 231.

The third experiment aims at obtaining the optimum material of theroller surface of the swing guide roller 220. More specifically, inFIGS. 6 and 7, as the material of the roller surface, aluminum, which isthe material of the roller itself, was employed. In contrast to this, inthe third experiment, the polarization dispersion of the optical fiber200 was measured while changing the material of the roller surfacevariously. Various other conditions were the same as in the casedescribed with reference to FIGS. 6 and 7, except that the swing periodof the swing guide roller 220 was changed between 0 and 200 rpm.

The graph of FIG. 12 shows the result of the third experiment. When theswing guide roller 220 is not swung at all, no difference inpolarization dispersion resulted from the difference in material of theroller surface. In contrast to this, as is apparent from this graph,when the swing guide roller 220 is swung, the polarization dispersion ofthe optical fiber 200 is decreased in the entire swing period in theorder of an urethane resin, an acrylic resin, aluminum, and Bakelitethat are employed as the materials of the roller surfaces. Inparticular, in the swing period of 20 to 150 rpm, the decrease inpolarization dispersion of the optical fiber 200 is the largest with theurethane resin, and the second largest with the acrylic resin. Thepreferred swing period is 50 to 100 rpm.

The effect of decreasing the polarization dispersion of the opticalfiber 200 corresponds to the magnitude of the coefficient of friction ofthe material of the roller surface against the resin coating 190 appliedon the surface of the optical fiber 200. More specifically, the higherthe coefficient of friction of the material of the roller surfaceagainst the resin coating 190 on the surface of the optical fiber 200,the more ideal rolling of the optical fiber 200 without sliding on theroller surface. This rolling imparts a twist to the optical fiber 200,thereby decreasing the polarization dispersion of the optical fiber 200.

Accordingly, from the third experiment, it is confirmed that the rollersurface of the first guide roller 220 with which the optical fiber 200is brought into contact is preferably covered with a resin having a highcoefficient of friction against the resin coating 190 of the opticalfiber 200, and that an urethane resin or an acrylic resin is suitable asthis resin.

The fourth experiment aims at obtaining the relationship between therolling properties on the roller surface of the swing guide roller 220and the drawing tension of the optical fiber 200. More specifically, asthe material of the roller surface, aluminum, which is the material ofthe roller itself, was employed, as shown in FIGS. 6 and 7, and theswing period was set to 100 rpm. Rolling frequencies were observed whilechanging the drawing tension. The optical fiber 200 with the coating wasset to 250 μm.

The graph of FIG. 13 shows the result of the fourth experiment. As isapparent from this graph, an improvement in rolling properties appearswhen the drawing tension is 4.0 kg/mm² or more. Fiber disconnectionoccurs when the drawing tension exceeds 16 kg/mm².

As a result, from the fourth experiment, it is confirmed that thedrawing tension of the optical fiber 200 is preferably 4.0 kg/mm² ormore and 16 kg/mm² or less.

The fifth experiment aims at obtaining the optimum conditions for therelative position of the pair of guide rollers 210 for optical fiberswing suppression, that rotate freely in the traveling direction of theoptical fiber 200, with respect to the swing guide roller 220, and thegap between the pair of guide rollers 210. More specifically, as shownin FIG. 14, by employing a vertical distance L (L=30 mm, 50 mm, 100 mm,and 200 mm) between the swing guide roller 220 and one of the pair ofguide rollers 210 as the parameter, a gap d between the pair of guiderollers 210 was changed from 1 mm to 8 mm. The polarization dispersionof the optical fiber 200 obtained in this case was measured. Variousother conditions were the same as in the case described with referenceto FIGS. 6 and 7. In order to confirm the effect obtained by allowingfree rotation of the pair of guide rollers 210 in the travelingdirection of the optical fiber 200, the polarization dispersion wasmeasured also in a case wherein the guide rollers 210 were fixed not tobe rotatable.

The graph of FIG. 15 shows the result of the fifth experiment. As isapparent from this graph, the shorter the vertical distance L betweenthe swing guide roller 220 and the pair of guide rollers 210, thesmaller the polarization dispersion of the optical fiber 200, and thesmaller the gap d between the pair of guide rollers 210, the smaller thepolarization dispersion of the optical fiber 200. In particular, whenL=30 mm, the polarization dispersion is decreased largely regardless ofd. When L=50 mm, the polarization dispersion is largely decreased withd=1 mm to 2 mm.

This means that the pair of guide rollers 210 suppress the responsivemotion of the optical fiber 200 that occurs in response to the swing ofthe swing guide roller 220, thereby suppressing a decrease in amount oftwist of the optical fiber 200 which is caused by the responsive motionof the optical fiber 200. The shorter the vertical distance L betweenthe swing guide roller 220 and the pair of guide rollers 210, and thesmaller the gap d between the pair of guide rollers 210, the larger theeffect of suppressing the responsive motion of the optical fiber 200.Thus, the effect of decreasing the polarization dispersion of theoptical fiber 200 may also be increased accordingly due to this.

When the pair of guide rollers 210 are set not to be rotatable, thepolarization dispersion of the optical fiber 200 is generally largerthan in a case wherein the pair of guide rollers 210 are rotatableregardless of the magnitude of the distance L. However, the larger thegap d, the smaller the polarization dispersion of the optical fiber 200.When d=10 mm, there is substantially no difference in polarizationdispersion when compared to the case wherein the pair of guide rollers210 are rotatable.

A non-uniformity ratio in thickness of the optical fiber 200 coated withthe resin coating 190 was measured under the same conditions as those ofthe fifth experiment. Note that when the non-uniformity ratio inthickness is 0%, the sectional shapes of the core portion and thecladding portion of the optical fiber 200 become perfectly circular andconcentric. Although the result of measurement is not shown in thegraph, when the gaps d=1 mm, 2 mm, 5 mm, 8 mm, and 10 mm, thenon-uniformity ratios in thickness was 15%, 20%, 35%, 40%, and 45%,respectively, regardless of the magnitude of the distance L. Morespecifically, the smaller the gap d, the lower the non-uniformity ratioin thickness, and the less the non-uniformity in thickness of theoptical fiber 200 coated with the resin coating 190.

This may be because the smaller the gap d between the pair of guiderollers 210, the more the responsive motion of the optical fiber 200 issuppressed, and the smoother the optical fiber 200 can roll on theroller surface of the swing guide roller 220. The non-uniformity ratioin thickness of the optical fiber 200 coated with the resin coating 190may be decreased by smooth rolling of the optical fiber 200.

Accordingly, the following facts are confirmed from the fifthexperiment. The pair of guide rollers 210 for optical fiber responsivemotion suppression which rotate freely in the traveling direction of theoptical fiber 200 help the optical fiber 200 to roll smoothly on theroller surface of the swing guide roller 220, thereby imparting a twistto the optical fiber 200 highly efficiently in accordance with the swingspeed of the swing guide roller 220. The smaller the vertical distance Lbetween the pair of guide rollers 210 and the swing guide roller 220,and the smaller the gap d between the pair of guide rollers 210, thenthe larger the effect of helping imparting the twist. Also, thenon-uniformity in thickness of the optical fiber 200 coated with theresin coating 190 is decreased. The smaller the gap d between the pairof guide rollers 210, the larger the thickness non-uniformity decreasingeffect.

As has been described above in detail, the optical fiber manufacturingmethod of the present invention comprises the first substep of guidingthe optical fiber with the first guide roller whose rotating shaftswings periodically, and rolling the optical fiber on the roller surfacein accordance with swing of the first guide roller, and the secondsubstep of guiding the optical fiber that has passed through the firstguide roller with the second guide roller provided to a next stage ofsaid first guide roller and having a fixed rotating shaft, andsuppressing the optical fiber from rolling on a roller surface of thesecond guide roller with the optical fiber rolling suppression meansprovided to the second guide roller, thereby imparting a predeterminedtwist to the optical fiber effectively.

If the manufacturing method further comprises the substep of suppressinga responsive motion of the optical fiber, which is caused by the swingof the first guide roller, with an optical fiber responsive motionsuppressing means provided on a preceding stage of the first guideroller, a predetermined twist can be imparted to the optical fiber moreeffectively, and the non-uniformity in thickness of the coating of theoptical fiber can be suppressed.

Furthermore, as the optical fiber of the present invention ismanufactured in accordance with the above manufacturing method and isimparted with a predetermined twist, even if the sectional shapes of itscore portion and cladding portion are not perfectly circular andconcentric, polarization dispersion can be suppressed in the elongatedoptical fiber as a whole equivalently as in a case wherein the coreportion and the cladding portion are perfectly circular and concentric.Since the non-uniformity in thickness of the coating of the opticalfiber is suppressed, the stress distribution on the section of theoptical fiber can be prevented from being asymmetric, thereby increasingthe strength of the optical fiber when formed into a cable.

Embodiment 2

An apparatus for swinging the swing guide roller 220 will be described.It is ideal that the swing guide roller 220 swing sinusoidally. Morespecifically, it is ideal that a swing angle θ (see FIG. 7) of the swingguide roller 220 change sinusoidally as a function of time. At least,the change over time of the swing angle θ must be such that the maximumclockwise angle and the maximum counterclockwise angle are equal, thatthe period of the clockwise swing and the period of the counterclockwiseswing are equal, and that the swing angular velocity changes smoothly.These conditions are required as the change over time of the swing angleθ. Then, when the optical fiber is formed into a cable, a kink will notbe formed, thereby preventing the optical fiber from being easilyfractured.

FIG. 16 is a perspective view of an example of a mechanism that swingsthe swing guide roller 220 such that the swing angle θ changessinusoidally. A gear 510 is rotatably mounted on a base 500 with itsrotating shaft being directed vertically. A roller base 520 is mountedon the upper surface of the gear 510, and the swing guide roller 220 isrotatably mounted on a rotating shaft 530 projecting from the 510 rollerbase 520 horizontally.

A movable portion 550 is mounted on the base 500 through a first linearguide 540. Accordingly, the movable portion 550 can move in apredetermined direction with respect to the base 500. A base portion 570of a second linear guide 560 is fixed to the movable portion 550. Thesecond linear guide 560 is movable along the base portion 570. Themoving direction of the first linear guide 540 is perpendicular to themoving direction of the second linear guide 560. One end of an arm 580is fixed to the second linear guide 560, and the other end of the arm580 is rotatably mounted on a pin 600 projecting from a rotary disk 590.The rotary disk 590 is mounted on the output shaft of a motor 700 and areduction gear 710 and is rotated. A rack gear 610 is fixed to themovable portion 550, and the rack gear 610 meshes with the gear 510.

The operation of the mechanism shown in FIG. 16 will be described.First, the rotary disk 590 is rotated by the output from the motor whichis decelerated by the reduction gear. This rotation rotates the pin 600in turn, and one end of the arm 580 moves along a circumference. Sincethe arm 580 is mounted on the base 500 through the two linear guides 540and 560, it does not rotate with respect to the base 500. Accordingly,the other end of the arm 580 also moves along the circumference, so thatthe second linear guide 560 also moves along the circumference. Sincethe base portion 570 of the second linear guide 560 can move only in apredetermined linear direction (i.e., in the moving direction of thefirst linear guide 540), its position changes sinusoidally. The positionof the movable portion 550 to which the base portion 570 is fixed alsochanges sinusoidally, so that the position of the rack gear 610 alsochanges in the same manner. Accordingly, the rotation angle of the gear510 changes sinusoidally, so that the swing angle θ of the swing guideroller 220 mounted to the gear 510 also changes sinusoidally.

FIGS. 17A to 17D show plan views of the optical fiber drawing apparatusin each steps in fiber drawing viewed from a top of the apparatus, thatis, from optical fiber feeding direction.

FIG. 17A shows a status that the pin 600 is located in right sideagainst a center of the rotary disk 590. In this status, the firstmovable portion 550 is located in a substantially center of a strokethereof. In this status, the rack gear 610 is also located insubstantially center of the stroke thereof and an angle of the piniongear 510 is the same as an center angle of the swing range thereof.Accordingly, a swing angle θ of the swing guide roller is substantiallyzero.

Next, the motor 700 rotates at a constant velocity and the rotary plate590 is rotated in a counterclockwise direction by about 90 degree by adriving power transmitted from the motor 700 through the reduction gear710. This status is shown in FIG. 17B. As shown in FIG. 17B, the pin 600is located in an upper position of a center of the rotary plate 590, theposition of the first movable portion 550 is substantially identical toone of a maximum stroke position, the position of the rack gear 610 issubstantially identical to one of the maximum stroke position, and anangle of the pinion gear 510 is substantially identical to one ofmaximum swing angle. Accordingly a swing angle θ of the swing guideroller 220 becomes maximum.

Further, the motor 700 rotates at a constant velocity and the rotaryplate 590 is further rotated in a counterclockwise direction by about 90degree by a driving power transmitted from the motor 700 through thereduction gear 710. This status is shown in FIG. 17C. As shown in FIG.17C, the pin 600 is located in an left side of a center of the rotaryplate 590, the position of the first movable portion 550 is located in acenter of the stroke thereof again, an angle of the rack gear 610 islocated in a center of the stroke thereof again, and an angle of thepinion gear 510 becomes a center angle of the swing range thereof again.Accordingly a swing angle θ of the swing guide roller 220 becomes zeroagain.

More further the motor 700 rotates at a constant velocity again and therotary plate 590 is rotated in a counterclockwise direction by about 90degree by a driving power transmitted from the motor 700 through thereduction gear 710. This status is shown in FIG. 17D. As shown in FIG.17D, the pin 600 is located in a lower position of a center of therotary plate 590, the position of the first movable portion 550 issubstantially identical to the other of a maximum stroke position again,the position of the rack gear 610 is substantially identical to theother of the maximum stroke position again, and an angle of the piniongear 510 is substantially identical to one of maximum swing angle.Accordingly a swing angle θ of the swing guide roller 220 becomesmaximum and a sign of the swing angle is opposite to that shown in FIG.17B.

The period of the swing of the swing guide roller is set preferably tobe 20 to 150 rpm and further preferably to be set 50-100 rpm. This isbecause in this range of the swing period, the polarization dispersionof the result optical fiber 200 effectively decreases.

Besides, it is important that in the drawing, the drawing optical fiberdoes not come in contact with any portion of the roller 220, especiallya flange thereof and further, the change of the swing should be smoothlyand the time period during the swing direction changes should be zero.

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

The basic Japanese Applications No. 7-041820 (041820/1995) filed on Mar.1, 1995, No. 7-281809 (281809/1995) filed on Oct. 30, 1995 and 8-057881(057881/1996) filed on Mar. 14, 1996 are hereby incorporated byreference.

What is claimed is:
 1. An optical fiber manufacturing methodcomprising:drawing an optical fiber from an optical fiber preform;coating said optical fiber with a predetermined coating material; andimparting a predetermined twist to said optical fiber coated with saidpredetermined coating material, this twist imparting step comprising thesteps of:guiding said optical fiber coated with said predeterminedcoating material with a first guide roller that swings periodically, androlling said optical fiber on a roller surface of said first guideroller in accordance with swing of said first guide roller; suppressingresponsive motion of said optical fiber, which is caused by the swing ofsaid first guide roller, with an optical fiber responsive motionsuppressing portion provided on a preceding stage of said first guideroller; and guiding said optical fiber that has passed through saidfirst guide roller to a second guide roller having a fixed rotatingshaft and suppressing said optical fiber from rolling on a rollersurface of said second guide roller with an optical fiber rollingsuppression portion provided to said second guide roller; wherein saidoptical fiber responsive motion suppressing portion is at least one pairof guide rollers which are provided above said first guide roller at apredetermined distance to oppose each other at a predetermined gapthrough which said optical fiber is passed.
 2. An optical fibermanufacturing method comprising:drawing an optical fiber from an opticalfiber preform; coating said optical fiber with a predetermined coatingmaterial; and imparting a predetermined twist to said optical fibercoated with said predetermined coating material, said impartingcomprises:first guiding said optical fiber coated with saidpredetermined coating material with a first guide roller that swingsperiodically, and rolling said optical fiber on a roller surface of saidfirst guide roller in accordance with swing of said first guide roller;and second guiding said optical fiber that has passed through said firstguide roller to a second guide roller having a fixed rotating shaft andsuppressing said optical fiber from rolling on a roller surface of saidsecond guide roller by providing that a position of said optical fiberis not substantially shifted on said second roller in a directionparallel with a longitudinal direction of said fixed rotating shaft,wherein said step of second guiding is provided by contacting fittinglysaid optical fiber on two sides thereof with a groove formed in saidsecond guide roller.
 3. The method according to claim 2, wherein anouter diameter and position of each of said first and second guiderollers are adjusted, so that a length with which said optical fibercontacts said roller surface of said first guide roller is substantiallyequal to a roller circumference corresponding to a central angle of 90°of said first guide roller.
 4. The method according to claim 2, whereinan outer diameter and position of each of said first and second guiderollers are adjusted, so that a length with which said optical fibercontacts said roller surface of said first guide roller is smaller thana roller circumference corresponding to a central angle of 90° of saidfirst guide roller.
 5. The method according to claim 2, wherein the stepof first guiding includes guiding said optical fiber on said rollersurface of said first guide roller with which said optical fiber isbrought into contact and which is covered with a resin having acoefficient of friction against said predetermined coating material ofsaid optical fiber wherein the friction prevents said optical fiber fromsliding on said roller surface.
 6. The method according to claim 5,wherein said resin to cover said roller surface of said first guideroller is an urethane resin.
 7. The method according to claim 5, whereinsaid resin to cover said roller surface of said first guide roller is anacrylic resin.
 8. The method according to claim 2, wherein said opticalfiber has a drawing tension of not less than 4.0 kg/mm² and not morethan 16 kg/mm².
 9. The method according to claim 2, wherein said step ofimparting a predetermined twist to said optical fiber further comprisesthe substep of suppressing responsive motion of said optical fiber,which is caused by swing of said first guide roller, with an opticalfiber responsive motion suppressing portion provided on a precedingstage of said first guide roller.
 10. The method according to claim 2,wherein in said step of second guiding, the groove is a V-shaped grooveformed in the roller surface of said second guide roller in which saidoptical fiber is fitted, said optical fiber being contacted with sidesof the V-shaped groove, wherein an outer diameter and position of eachof said first and said second guide rollers are adjusted so that alength with which said optical fiber contacts the roller surface of saidfirst guide roller is smaller than a roller circumference correspondingto a central angle of 90 degrees of said first guide roller.